Fiber-reinforced composites and methods of forming and using same

ABSTRACT

A method of forming fiber-reinforced composites. The method includes stabilizing two or more carbon fibers tows together (a) with a stabilizing resin and (b) in-line with a commercial carbon fiber production process to form a semi-finished tape; and impregnating the semi-finished tape with a matrix resin in a process offline of the carbon fiber production process to form a prepreg.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application Ser.No. 62/639,409 filed Mar. 6, 2018, the disclosure of which is herebyincorporated in their entirety by reference.

TECHNICAL FIELD

The present disclosure relates to fiber-reinforced composites andmethods of forming and using same.

BACKGROUND

Fiber-reinforced composites may generally include a resin and areinforcing fiber. In many cases, the resin and the reinforcing fiberhave different properties, such that when these components are combined,the resulting fiber-reinforced composite has properties intermediate theresin and the reinforcing fiber. For example, the resin may berelatively low strength but may have relatively high elongationproperties, while the reinforcing fiber may be relatively high strengthbut may be relatively brittle. A part derived from a composite materialmay have a strength that is greater than the resin while also beingrelatively tough compared to the reinforcing fiber.

SUMMARY

In one embodiment, a method of forming fiber-reinforced composites isdisclosed. The method includes stabilizing two or more carbon fiberstows together (a) with a stabilizing resin and (b) in-line with acommercial carbon fiber production process to form a semi-finished tape;and impregnating the semi-finished tape with a matrix resin in a processoffline of the carbon fiber production process to form a prepreg.

In another embodiment, a method of forming fiber-reinforced compositesis disclosed. The method includes stabilizing a carbon fiber tow havinga filament count of greater than or equal to 12K and a filament densityof less than or equal to 1,000 filaments/mm (a) with a stabilizingmaterial and (b) in-line with a commercial carbon fiber productionprocess to form a semi-finished tape; and impregnating the semi-finishedtape with a matrix resin in a process offline of the carbon fiberproduction process to form a fiber-reinforced composite.

In yet another embodiment, a method of forming fiber-reinforcedcomposites is disclosed. The method includes vertically separating oneor more groups of carbon fiber tows onto one or more elevations,respectively; stabilizing the one or more groups of carbon fiber towstogether at their respective elevations (a) with a stabilizing resin and(b) in-line with a commercial carbon fiber production process to formone or more semi-finished tapes; and impregnating the one or moresemi-finished tapes with a matrix resin in a process offline of thecarbon fiber production process to form a prepreg.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a schematic, side view of a carbon fiber productionprocess according to a first embodiment.

FIG. 2 depicts a schematic, top view of a carbon fiber productionprocess according to the first embodiment.

FIG. 3 depicts a schematic, fragmented, perspective view of a carbonfiber elevation separation step according to the first embodiment.

FIG. 4 depicts a schematic, side view of a carbon fiber productionprocess according to a second embodiment.

FIG. 5 depicts a schematic, top view of a carbon fiber productionprocess according to the second embodiment.

FIG. 6 depicts a schematic, fragmented, perspective view of a carbonfiber elevation separation step according to the second embodiment.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described herein. It is to beunderstood, however, that the disclosed embodiments are merely examplesand other embodiments can take various and alternative forms. Thefigures are not necessarily to scale; some features could be exaggeratedor minimized to show details of particular components. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a representative basis forteaching one skilled in the art to variously employ the embodiments. Asthose of ordinary skill in the art will understand, various featuresillustrated and described with reference to any one of the figures canbe combined with features illustrated in one or more other figures toproduce embodiments that are not explicitly illustrated or described.The combinations of features illustrated provide representativeembodiments for typical applications. Various combinations andmodifications of the features consistent with the teachings of thisdisclosure, however, could be desired for particular applications orimplementations.

The term “about” may be used herein to describe disclosed or claimedembodiments. The term “about” may modify a value disclosed or claimed inthe present disclosure. In such instances, “about” may signify that thevalue it modifies is within ±0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or 10%of the value.

Among reinforcing fibers, the specific strength and stiffness of carbonfiber is among the highest. For example, compared to E-glass, a widelyused industrial fiber, the specific strength of carbon fiber can be morethan twice as high while the specific modulus can be over four timeshigher. For industries where fuel economy, performance, and/orgreenhouse gas emissions are highly relevant (e.g., aerospace andautomotive industries), carbon fibers composites (i.e., fiber-reinforcedcomposites made from carbon fiber) may be particularly beneficial.However, the cost of converting carbon fiber into a part remains highand presents a hurdle to the use of carbon fiber composites.Consequently, process refinements to improve efficiency, eliminatewaste, and/or reduce cost may expand the value and market for carbonfiber composites.

Carbon fiber may be used in a prepreg (an example of a fiber-reinforcedcomposite) in the production of parts. The carbon fiber, typically in acontinuous format such as unidirectional fibers, woven tows, or stitchedplies of unidirectional fibers, and the resin are pre-impregnated toform the prepreg in which the resin substantially impregnates the fibersand forms an intermediate material. The prepreg may be placed into amold to produce a part. Impregnation may refer to a process in which theresin and fiber are subjected to conditions that promote the wet-throughof the resin into the mass of the fibers and wets out the individualfilaments. This wet-out may refer to the resin coming into close enoughcontact with the filaments of the fiber so that the resin mechanicallycouples to the surface features of the individual filaments andchemically couples to the molecular structure of the filaments. Strongcoupling between the resin and the filament may provide optimumfiber-reinforced composite properties for structural applications.

Carbon fiber may be spread into a thin layer of filaments to reduce thedepth of filaments through which the resin passes to reach eachfilament. This spreading process may include drawing fiber from bobbinsin-line with the impregnation process. However, spreading of the carbonfiber in-line with the impregnation process may introduce additionalconversion costs for converting carbon fiber to produce a prepreg.

Carbon fiber may be produced as a relatively wide but thin band offilaments from a starting material of multiple strands of precursorfiber that are spread flat to form a tow band. A tow band may range fromabout 1,000 filaments or less for a scientific line, up to about 100 mmfor a microline, about 300 to 1,000 mm for a pilot line, and about 1 mto 5 m or 6 m or higher for a commercial production line. Each strand ofprecursor fiber may consist of a specified filament count, which may bereferred to as the tow size. The tow size may range from about 3K orlower to about 60K or higher, where K=1,000. Non-limiting examples ofspecific sizes include about 1K, 3K, 6K, 12K, 15K, 24K and 50K. Assuming50K tows are spaced every about 20 mm in width, then the filamentdensity would be about 2,500 filaments/mm. The filament density may behigher or lower for other configurations, filament diameters and towsizes. For example, filament densities of about 3,500 filament/mm ormore may be desired to increase line capacity.

The precursor fibers typically undergo a multi-step conversion processwhereby the fiber is initially stretched to orient its molecularstructure followed by a stabilization (thermosetting) process where thefiber is exposed to air at elevated temperatures. The stabilized fiberis then subjected to a series of elevated temperatures within an inertenvironment along a series of furnaces. This step is known ascarbonization. Upon exiting the furnace, the resulting carbon fiber mayundergo a surface treatment followed by the application of a sizingagent. After these steps are performed, the carbon fiber is typicallywound into a cylindrical package or bobbin, wrapped in film, andpackaged in boxes for shipment.

The surface treatment modifies the physical and/or chemical nature ofthe filaments of the carbon fiber exiting the furnace to improve themechanical and/or chemical coupling of the carbon fiber with the resin.The surface treatment may change the physical surface of the fiber, suchas etching the surface to promote mechanical coupling between thefilaments and the resin. The surface treatment may also increase thenumber of chemically reactive sites on the surface of each filament tofacilitate chemical coupling with the resin. The surface treatment mayalso improve wetting (e.g., impregnation or wet-out or coverage) of thefilaments by the resin. The surface treatment may deliver one or more ofthese effects.

Sizing agents are typically complex chemical mixtures applied tofilaments that contain a variety of constituents, for example, filmformers, coupling agents, resins, and/or other compounds. Sizing agentsmay be typically applied as a dispersion or solution using an organicsolvent or as an aqueous based solution or dispersion. Non-limitingfunctions of a sizing agent include (1) protecting filaments fromabrasion during subsequent handling, such as weaving, (2) control ofstatic electricity, and (3) promoting chemical coupling between thefilaments and resin applied during subsequent processing. Sizing differsfrom matrix resin in that a major function of a matrix resin is tofacilitate the transfer of load between the fibers and to protect thefiber from external forces or environmental damage. Moreover, a matrixresin may exhibit a higher strain to failure than the carbon fiber andmay contribute to the toughness of the composite material. Once dried,the sizing tends to weakly hold the individual filaments together.

Methods that utilize carbon fiber (e.g., as continuous fibers or fiberspre-impregnated with resin) typically include a process to spread carbonfiber tows coming from a bobbin. The spreading process serves one ormore functions. First, the individual filaments may be separated fromeach other if a sizing agent has been applied to facilitate impregnationor surrounding each filament with resin. The sizing may inhibit theability of the resin to surround individual filaments because sizing mayhold the filaments together. Second, the spreading process may modifythe profile of the tow to a thinner and wider band of filaments toincrease surface area or expose more filaments to the resin beingapplied to facilitate impregnation of the individual filaments.

The spreading process may have one or more drawbacks. Spreading is oftendone under tension using a series of spreader bars. The bars may beheated, stationary, rotating, vibrating, or use a combination of theseapproaches. The bars may be staggered causing the tows to partially wraparound each bar and drag across the surface. This may cause increasedtension over each successive bar. The interaction between the tows andbars under tension to separate the filaments to overcome the effects ofthe sizing can damage the filaments causing breakage or microcracksweakening the filaments when stressed as a composite material or part.The spreading process may also add complexity and cost to the process ofconverting the carbon fiber tows into intermediate formats. Thespreading process may be rate limiting, thereby adding a bottleneck tothe process. Such bottleneck may contribute to higher manufacturingcosts for downstream processes, such as impregnation.

Another method of spreading utilizes a stream of air applied across thetows to influence a spreading behavior. Such a technique may reduce thedamage experienced by mechanical manipulation of the fiber, but addscomplexity and expense to the process, and limits the speed ofdownstream processes.

Considering one or more of these drawbacks, one or more embodiments areproposed. The proposed processes separate the spreading of the tow fromthe impregnation step and places the production of the spread tow andits stabilization for subsequent use upstream with the commercialproduction of the carbon fiber, thereby reducing the conversion cost ofproducing the fiber-reinforced composite (e.g., prepreg or filamentwinding). In one or more embodiments, a process includes a first step ofconverting carbon fiber tow into a semi-finished tape in-line with thecommercial production of the carbon fiber and a second step ofimpregnating the semi-finished tape with a matrix resin offline from thecommercial production of the carbon fiber.

Production of a semi-finished tape in accordance with one or moreembodiments can be accomplished in various ways. Carbon fiber tow, suchas about 3K, 6K, 12K, 24K, and 50K carbon fiber tow, may be used to bedirectly stabilized into a semi-finished tape. The carbon fiber tow maybe spread further in-line with the carbon fiber production process intoa desired tape format or structure before being stabilized to eliminategaps between the tows or to reduce the filament density to a levelsuitable for the impregnation process without the need for additionalspreading.

For example, 50K carbon fiber tows may be produced at a filament densityof 2,500 filaments/mm and the impregnation process may require afilament density of around 833 filaments/mm necessitating additionalspreading of the tows before stabilization. In one embodiment, thecarbon fiber tows may be separated onto three different elevations. Thedifferently elevated tows may be spread from a first width (e.g., 20 mm)to a second width (e.g., 60 mm) to produce a uniform tape or sheetformat. By utilizing this method, the horizontal alignment of the towcenterlines remains unaltered minimizing the disruption of tensionacross the fiber through the fiber production process. Each set of towscan be spread and combined at a different elevation so that three tapestructures can be produced at the same time. For less spreading, everyother tow may be separated and two tape structures producedsimultaneously. For more spreading, every fourth or fifth tow may beseparated and a corresponding number of tape structures produced at thesame time. In one embodiment, only one tape structure may be producedfrom the selected tows and those not utilized can be processed undernormal conditions and packaged into bobbins.

One or more methods can be used to stabilize the carbon fiber. Onemethod is to utilize a stabilizing material such as a sizing agent insufficient concentration so that when the sizing is dried it retains thefiber in a tape format and facilitates winding onto and unwinding from aspool. Alternatively, it may be advantageous to eliminate or minimizethe amount of sizing applied. In such a case, the stabilizing materialcould be a resin such as a binder applied to the fiber. The applicationof the binder (an example of a stabilizing resin) may coincide with theapplication of the sizing agent or could be applied separately. If athermoset binder is utilized, then curing, partial curing, or meltingand cooling of the binder after application stabilizes the fiber in theformat of the semi-finished tape. If a thermoplastic binder is used asthe stabilizing agent, then then the binder may be melted and cooled tostabilize the fiber into the format of a semi-finished tape. Thisthermoplastic binder could become a portion of all the matrix resin thatimpregnates the filaments during the impregnation step or the bindercould constitute all of the matrix resin following the impregnationstep.

Alternatively, or in addition to the sizing and/or binder, a separateapplication of a stabilizing resin in a suitable format can be combinedwith the carbon fiber thereby stabilizing and/or protecting the fiberfor spooling and unspooling. The stabilizing resin could be similar tothe binder in composition and physical properties or different from thebinder. In the case of a thermoplastic binder, the binder may have adifferent melting point from the resin. The stabilizing resin may beapplied to one or both sides of the carbon fiber. This stabilizing resincan become a portion of or all of the matrix resin that impregnates thefilaments during the impregnation step. The stabilizing resin, forexample, could be in the format of a nonwoven fabric or film and maysimply act as a divider in the first step to facilitate spooling orwinding onto a core so that adjacent layers of the thinly spaced fibersdo not interact with each other and the semi-finished tape can beunwound without damage for subsequent processing. During theimpregnation step, this nonwoven fabric or film would become part or allof the matrix resin. Another possibility to stabilize the fiber includesthe use of an impregnating agent possibly containing a microcrystallinewax with a lower melting point than the resin and low viscosity toeasily permeate the filaments when melted and adhere to both thestabilizing resin, such as a nonwoven, and filaments when cooled.

If a sizing agent has been applied to the fiber, the concentration ofthe sizing is typically less than 10% weight fraction of the fiber andmore typically less than about 5% and usually less than about 3%. If astabilizing resin is utilized in the production of the semi-finishedtape that through subsequent impregnation becomes some or all the matrixresin of the composite material it can be applied at a concentration upto about 80% volume fraction based upon the fully impregnated prepreg orbetween about 40% and 60% volume fraction based upon the fullyimpregnated prepreg. Resin volume fraction based upon fully impregnatedprepreg is a theoretical calculation of the percentage of resin volumeto total volume of the composite material which includes the volumerepresented by the fiber but excluding any voids (spaces occupied byair).

If a stabilizing resin is utilized in the production of a semi-finishedtape, it can be converted in a separate or offsite process into a formatsuitable for bringing it into proximity with the carbon fiber. The resincan be a thermoplastic or thermoset resin or a combination of the twoand may include additives, fillers, or other compounds that contributethe desired attributes required for subsequent processing and/or use inthe intended application. Such formats may include powders, suspensions,solutions, continuous tows or yarns formed from filaments produced fromthe resin, nonwoven mats derived from said filaments or as a spunbond,or textile type fabrics produced from weaving or stitching together saidfilaments or yarns. Another format may include of one or more filmsproduced from the resin, or a combination of formats could be applied.

Once the carbon fiber has been stabilized as a semi-finished tape, thesemi-finished tape is packaged for transportation to and for use in asubsequent impregnation process. The packaging of the semi-finished tapemay be in the form of a spool onto which the semi-finished tape iswound. If the semi-finished tape is in the format of a single spreadtow, then the packaging could be in the format of a bobbin. Ifnecessary, the packaging can include a protective layer of film or a bagthat surrounds the spool or package or bobbin and forms a barrier tomoisture or other contaminants that may adversely affect the resin orfiber or its suitability for subsequent processing.

In the second step, the semi-finished tape undergoes impregnation bysubjecting it to conditions suitable for penetrating the fiber with amatrix resin and impregnating or surrounding the desired portion offilaments with said resin. If the semi-finished tape is prepared withoutsufficient stabilizing resin to produce the targeted fiber concentrationfor the prepreg or finished part, then additional matrix resin in asuitable format and formulation can be applied. If a thermoplasticprepreg is being produced, these formats may include powders, nonwovens,solutions, suspensions, films, and melt streams of molten resin. If athermoset prepreg is being produced, the formats may include powders,films, liquids, solutions, suspensions, and pastes.

The second step may utilize steps associated with the production ofprepreg, such as melt impregnation where molten polymer is applied tothe fiber, solution coating where a polymer is dissolved in a solventthrough which the fiber is drawn, slurry coating where polymer particlesare suspended in a solution through which the fiber is drawn, filmstacking where adjacent layers of un-melted polymer are initiallyapplied, filament winding where fiber is drawn through a resin bath,powder impregnation where dry particles of a resin are directly appliedto the fiber, or other suitable impregnation processes.

In one or more embodiments, a process includes a first step ofconverting a carbon fiber into a semi-finished tape in-line with thecommercial production of the carbon fiber and a second step ofimpregnating the semi-finished tape with matrix resin offline from theproduction of the carbon fiber. This process has several advantages overa process in which the carbon fiber is spread in-line with theimpregnation process.

First, the production of carbon fiber is done at a relatively slow speedfacilitating the addition of the conversion of the carbon fiber into asemi-finished tape in-line. Typical line speeds to produce carbon fiberare in the range of about 6 to 12 m/min. Various spreading technologieshave similar processing speeds. The processing speeds for stabilizingcarbon fiber into a tape format are also typically within this range.The stabilizing step adds relatively minor complexity and investment,and therefore, only minor costs are added by such integration.

Second, the issue of spreading the tow is reduced since the filamentscoming from the production process are loosely aligned but remainindependent of adjacent filaments, thereby permitting easy spreading ifnecessary depending upon the filament density targeted by theimpregnation process. Alternatively, if the filament density issatisfactorily coming off the production process, then the fiber can bestabilized directly into a tape format without the need for additionalspreading.

Third, the possibility exists to bypass the application of a sizingagent if an un-sized format is utilized. For certain matrix resins, anun-sized fiber may offer performance advantages as the un-sized fibercouples better to the resin than a fiber with a sizing agent. Forexample, a surface treatment applied to a carbon fiber may be veryeffective in promoting coupling between carbon fiber filaments and thematrix resin. However, due to handling issues associated with theutilization of carbon fiber post-production in traditional processessuch as weaving, an economical throughput often requires sizing. Whilesizing may promote coupling and facilitate handling, it sometimesreduces performance compared to un-sized but surface treated fiber. Asanother benefit, eliminating the use of sizing eliminates the associatedcosts. Alternatively, if sizing is warranted, converting the fiber intoa semi-finished tape in-line with the production of the fiber andapplication of the sizing agent enables the fiber to be retained in apreferential tape format or filament density as the sizing dries.Certain spreading techniques, such as an ultrasonic process in anaqueous based solution or other solution, may be compatible with thesizing process and/or surface treatment. Binders may be incorporatedwith the sizing to stabilize the format of carbon fiber into a tape orsheet.

The process of impregnation brings the matrix resin into direct contactwith and ideally surrounds each filament and promotes coupling of thetwo components. The coupling correlates to desirable properties of theresulting composite material. However, the impregnation process may beexpensive and complex. Such complexity may not be supported byattempting to impregnate in-line with the production of the carbonfiber. Such impregnation may be better conducted off-line of the carbonfiber production process in a subsequent process step.

In the case of producing a prepreg, an intermediate material in whichthe filaments are substantially impregnated before being converted intoa part, process parameters such as fiber tension, fiber temperature,resin temperature, applied pressure or shear, time at temperature andpressure, cooling time, and other process variables may require precisecontrol. The equipment necessary to achieve such control can represent asubstantial investment and therefore may be designed to operate atspeeds (meters/minute or feet/minute) higher than what can be achievedin the production of the carbon fiber to minimize amortized cost. Forexample, speeds more than about 12 m/min may be desired. In addition,such prepreg lines typically occupy significant space that would bedifficult to accommodate in-line at most existing carbon fiber plants orwithout significant additional investment. Also, the complexity ofoperating such a system in-line with the production of the carbon fibermay impede precise and consistent control of the carbon fiber productionprocess and resultant product characteristics and risk increased scrap,waste, and/or downtime. For example, precise control of tension duringthe process of producing carbon fiber is critical to establishingconsistent mechanical properties of the fiber. Precise control overtension may be compromised or the optimum tension for the production ofthe carbon fiber may be different from the optimum tension forimpregnating the fiber.

In one or more embodiments, conversion of the carbon fiber into asemi-finished tape in-line with the carbon fiber production process andcompletion of the impregnation of the semi-finished tape off-line in aseparate process under the controls and throughputs relevant to theimpregnation process is disclosed. One benefit of the semi-finished tapeis that the raw materials may be prepositioned into an optimumconfiguration to facilitate impregnation allowing impregnation to takeplace more economically and without undue stress on the fiber. Undersuch a scenario, impregnation can happen in a variety of methods thatapply heat and pressure and shear to wet-out the individual filamentswith resin. Heating can be from a variety of mechanisms such asinfrared, convection, conduction, electromagnetic such as microwaves orother sources or combinations of methods and may heat the fiber or theresin which then conducts heat to the other or heats both the resin andfiber at the same time. Pressure and shear can also be applied in avariety of methods such as with nip rollers, double belt presses,kneading rollers, impregnation rollers across which the tape is drawnunder tension, twisting of the tape, vibration such as ultrasonics, andother means.

While a tow band may include a plurality of tows, any number of the towscan be converted into the semi-finished tape. If all the tows are notutilized, then the others can be processed in the traditional means andpackaged for example as bobbins of dry or sized fiber. When only one ortwo or a few of the tows are utilized to produce the semi-finished tape,the result is a narrow tape. If a substantial number of tows or all thetows are utilized then the result is a wide tape or sheet. The tapes orsheets may be packaged directly or subdivided by slitting or other meansprior to packaging. The width of the semi-finished tape can range from afew millimeters to as high as several meters depending upon the numberof tows utilized and the width of the tow band.

FIGS. 1-6 describe embodiments of a carbon fiber production processincluding a stabilization step. FIGS. 1-3 disclose a carbon fiberproduction process according to a first embodiment. FIGS. 4-6 disclose acarbon fiber production process according to a second embodiment. Carbonfiber production process 10 of FIGS. 1-3 and carbon fiber productionprocess 100 of FIGS. 4-6 share common process steps. Each process 10 and100 begins with the unspooling of a precursor material, such aspolyacrylonitrile (PAN), as shown by spool 12. The precursor fiber 14 isfed into a stretching device 16 to orientate the molecular structure ofthe precursor material. The precursor fibers are oriented into a towband and subjected to a thermosetting step 20, and subsequently acarbonization step 22 and a graphitization step 24.

As schematically shown in the Figures, there are twelve (12) tows 18a-18 l forming a tow band 26. Each tow may have a tow size, for exampleabout 1K, 3K, 6K, 12K, 15K, 24K and 50K. The total width 28 of the towband 26 may be about 1 m to 6 m, or about 0.25 m incrementstherebetween. In one example, if there are 100 50K carbon fiber towswithin a tow band and each tow is spaced 20 mm, the total width of thetow band may be about 2 m.

As shown in the Figures, tow band 26 is first subjected to a surfacetreatment 30 and then subsequently subjected to a sizing agent 32. Thetreated and sized tow band is fed between rollers or stationary bars 36.The surface treatment 30 includes drawing the tow band 26 into and outof a bath with a surface treatment material. The sizing 32 includesdrawing the tow band 26 into and out of a bath of sizing agent. As shownin the Figures, the drawing of the tow band 26 through the baths includethe tow bands contacting a number of touch points. Arrangement of thesetouch points into different elevations similar to those of the spreadingzones 37 and 39 can be used to spread the carbon fiber tows in place ofthe spreading zones 37 and 39 or in addition to the spreading zones 37and 39.

The output from the rollers or stationary bars 36 is spaced verticallyin spreading zone 37 or 39. With respect to FIGS. 1-3, rollers 38 a, 38b and 38 c place each carbon tow from the tow band 26 on a first, secondor third elevation 40 a, 40 b and 40 c, respectively. As shown in FIGS.1-3, the first carbon fiber tow 42 a is placed on the first, highestelevation 40 a, the second carbon fiber tow 42 b is placed on thesecond, middle elevation 40 b, and the third carbon fiber tow 42 c isplaced on the third, lowest elevation 40 c. This separation sequence canbe repeated for each successive carbon tow. As shown in FIGS. 1-3, the1^(st), 4^(th), 7^(th) and 10^(th) carbon fiber tows are placed on thefirst, highest elevation 40 a, the 2^(nd), 5^(th), 8^(th) and 11^(th)carbon fiber tows are placed on the second, middle elevation 40 b, andthe 3^(rd) 6^(th), 9^(th) and 12^(th) carbon fiber tows are placed onthe third, lowest elevation 40 c. While separating adjacent carbon fibertows is shown in FIGS. 1-3, non-adjacent carbon fiber tows may be placedon different elevations. Separated carbon fiber tows 43 a-c are spreadonto spreaders 44 a-c and 46 a-c, respectively, to fill the gaps createdbetween the individual tows being placed at different elevations, whilemaintaining the same or about the same parallelism to the horizontalmachine centerline 66. In the embodiment shown in FIGS. 1-3, thefilament density may be reduced by ⅔^(rd) the filament density of thecarbon fiber tows entering the rollers or stationary bars 36.

Another embodiment is shown in FIGS. 4-6. In FIGS. 4-6, the filamentdensity may be reduced by a half by using every other tow and placingthe carbon fiber tows on first and second elevations 50 a and 50 b. Asshown in FIGS. 4-6, the first carbon fiber tow 52 a is placed on thefirst, high elevation 50 a, and the second carbon fiber tow 52 b isplaced on the second, low elevation 50 b by using rollers 54 a and 54 b,respectively. This separation sequence can be repeated for eachsuccessive carbon tow. As shown in FIGS. 4-6, the 1^(st), 3^(rd),5^(th), 7^(th), 9^(th) and 11^(th) carbon fiber tows are placed on thefirst, high elevation 50 a, and the 2^(nd), 4^(th), 6^(th), 8^(th),10^(th) and 12^(th) carbon fiber tows are placed on the second, lowelevation 50 b. While separating adjacent carbon fiber tows is shown inFIGS. 4-6, non-adjacent carbon fiber tows may be placed on differentelevations. Separated carbon fiber tows 53 a and 53 b are spread ontospreaders 56 a and 56 b and 58 a and 58 b, respectively, to fill gapscreated between the individual tows being placed at differentelevations, while maintaining the same or about the same parallelism tothe horizontal machine centerline 66.

Separated and spread carbon fiber tows are stabilized with a stabilizingresin or stabilizing material as shown in box 60 to produce asemi-finished tape 62. The stabilizing resin or stabilizing material maybe the same material or a different material as the matrix resin used toimpregnate the semi-finished tape. The stabilizing resin may include oneor more binders, one or more impregnating agents, or a combinationthereof. The stabilizing resin may include one or more additives, one ormore fillers or combinations thereof. The stabilizing resin may beintroduced in a format of a powder, a suspension, a solution, a yarn, anonwoven mat, a textile fabric, a film, or combinations thereof duringthe stabilizing step. The stabilizing material may be one or more resinsor one or more sizing agents.

The semi-finished tape 62 may be wound onto one or more windings 64. Inone or more embodiments, the carbon production process ends upon thesemi-finished tape 62 being wound, and the impregnation process beginsupon unwinding the wound semi-finished tape 62. The unwoundsemi-finished tape is then impregnated with a matrix resin in a processoffline of the carbon fiber production process.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms encompassed by the claims.The words used in the specification are words of description rather thanlimitation, and it is understood that various changes can be madewithout departing from the spirit and scope of the disclosure. Aspreviously described, the features of various embodiments can becombined to form further embodiments of the invention that may not beexplicitly described or illustrated. While various embodiments couldhave been described as providing advantages or being preferred overother embodiments or prior art implementations with respect to one ormore desired characteristics, those of ordinary skill in the artrecognize that one or more features or characteristics can becompromised to achieve desired overall system attributes, which dependon the specific application and implementation. These attributes caninclude, but are not limited to cost, strength, durability, life cyclecost, marketability, appearance, packaging, size, serviceability,weight, manufacturability, ease of assembly, etc. As such, to the extentany embodiments are described as less desirable than other embodimentsor prior art implementations with respect to one or morecharacteristics, these embodiments are not outside the scope of thedisclosure and can be desirable for particular applications.

1-24. (canceled)
 25. A method comprising: providing a tow band includingfirst one or more carbon fiber tows and second one or more carbon fibertows, the first one or more carbon fiber tows are horizontally spacedfrom the second one or more carbon fiber tows; vertically separating thefirst one or more carbon fiber tows and the second one or more carbonfiber tows of the tow band onto first and second elevations,respectively, to form a first horizontal gap on the first elevation anda second horizontal gap on the second elevation, the second one or morecarbon fiber tows vertically aligned with the first horizontal gap, andthe first one or more carbon fiber tows vertically aligned with thesecond horizontal gap; spreading the first one or more carbon fiber towsat the first elevation; and stabilizing the first one or more carbonfiber tows together at the first elevation with a stabilizing resin toform a first semi-finished tape from the first one or more carbon fibertows.
 26. The method of claim 25, wherein the first one or more carbonfiber tows including first and second carbon fiber tows and the secondone or more carbon fiber tows including third and fourth carbon fibertows.
 27. The method of claim 26, wherein the first and second carbonfiber tows are non-adjacent to each other prior to the verticallyseparating step.
 28. The method of claim 26, wherein the first andsecond carbon fiber tows are adjacent to each other prior to thevertically separating step.
 29. The method of claim 25, furthercomprising subjecting the tow band to a surface treatment inline withthe vertically separating step, the vertically separating step isinitiated during or before the subjecting step.
 30. The method of claim25, further comprising subjecting the tow band to a sizing agent inlinewith the vertically separating step, the vertically separating step isinitiated before or during the subjecting step.
 31. The method of claim27, wherein the first and second carbon fiber tows are adjacent to eachother after the vertically separating step.
 32. The method of claim 25,further comprising impregnating the first semi-finished tape with amatrix resin to form a prepreg.
 33. The method of claim 32, wherein thestabilizing resin and the matrix resin are the same material.
 34. Themethod of claim 25, further comprising: spreading the carbon fiber towswithin the second one or more carbon fiber tows at the second elevation;and stabilizing the second one or more carbon fiber tows at the secondelevation with the stabilizing resin to form a second semi-finished tapefrom the second one or more carbon fiber tows.
 35. The method of claim34, further comprising winding the first semi-finished tape onto a firstspool and winding the second semi-finished tape onto a second spool. 36.A method comprising: feeding a tow band including first one or morecarbon fiber tows and second one or more carbon fiber tows, the firstone or more carbon fiber tows are horizontally spaced from the secondone or more carbon fiber tows; separating the first one or more carbonfiber tows and the second one or more carbon fiber tows of the tow bandonto first and second elevations, respectively, to form a firsthorizontal gap on the first elevation and a second horizontal gap on thesecond elevation, the second one or more carbon fiber tows verticallyaligned with the first horizontal gap, and the first one or more carbonfiber tows vertically aligned with the second horizontal gap; andhorizontally spreading the first one or more carbon fiber tows at thefirst elevation and the second one or more carbon fiber tows at thesecond elevation.
 37. The method of claim 36, further comprisingstabilizing the first one or more carbon fiber tows together and thesecond one or more carbon fiber tows together at their respective firstand second elevations with a stabilizing resin to form first and secondsemi-finished tapes from the first one or more carbon fiber tows and thesecond one or more carbon fiber tows, respectively.
 38. The method ofclaim 36, wherein the first one or more carbon fiber tows includingfirst and second fiber tows, the second one or more carbon fiber towsincluding third and fourth carbon fiber tows, and the tow band includingthe first, second, third and fourth carbon fiber tows.
 39. The method ofclaim 38, wherein the first one or more carbon fiber tows and the secondone or more carbon fiber tows are non-adjacent to each other prior tothe separating step.
 40. The method of claim 38, wherein the first oneor more carbon fiber tows and the second one or more carbon fiber towsare adjacent to each other prior to the separating step.
 41. The methodof claim 36, further comprising impregnating the first and secondsemi-finished tapes with a matrix resin to form a prepreg.
 42. Themethod of claim 41, wherein the stabilizing resin and the matrix resinare the same material.
 43. The method of claim 41, wherein thestabilizing resin and the matrix resin are different materials.
 44. Themethod of claim 36, wherein the tow band has a width of 1 to 6 meters.45. A method comprising: unspooling a precursor material; treating theprecursor material to form a tow band including first one or more carbonfiber tows and second one or more carbon fiber tows, the first one ormore carbon fiber tows are horizontally spaced from the second one ormore carbon fiber tows; separating the first one or more carbon fibertows and second one or more carbon fiber tows of the tow band onto firstand second elevations, respectively, to form a first horizontal gap onthe first elevation and a second horizontal gap on the second elevation,the second one or more carbon fiber tows vertically aligned with thefirst horizontal gap, and the first one or more carbon fiber towsvertically aligned with the second horizontal gap; and horizontallyspreading the first one or more carbon fiber tows at the first elevationand the second one or more carbon fiber tows at the second elevation.46. The method of claim 45, further comprising stabilizing the first oneor more carbon fiber tows together and the second one or more carbonfiber tows together at their respective first and second elevations witha stabilizing resin to form first and second semi-finished tapes fromthe first one or more carbon fiber tows and the second one or morecarbon fiber tows, respectively.
 47. The method of claim 46, furthercomprising winding the first semi-finished tape onto a first spool andwinding the second semi-finished tape onto a second spool, the firstspool is different than the second spool.
 48. The method of claim 46,further comprising impregnating the first and second semi-finished tapeswith a matrix resin to form a prepreg.
 49. The method of claim 48,wherein the stabilizing resin and the matrix resin are differentmaterials.
 50. The method of claim 48, wherein the stabilizing resin andthe matrix resin are the same material.
 51. The method of claim 45,further comprising orienting the precursor material into the tow band.52. The method of claim 45, wherein the treating step includes one ormore of thermosetting, carbonizing and graphitizing the precursormaterial.
 53. The method of claim 45, wherein the unspooling andseparating steps occur inline with each other.
 54. The method of claim45, wherein the treating and separating steps occur inline with eachother.